The present invention is directed to bicycle shift control devices and, more particularly, to shift control devices capable of mounting about the bicycle handlebar for rotation about the axis of the handlebar.
A conventional bicycle shift control device of the type which mounts on the handlebar of the bicycle for rotation about the axis of the handlebar has been disclosed, for example, in International Patent Publication W093/09993. In this publication, a shift member of sleeve form is fit over the peripheral surface of the handlebar adjacent to a grip that has been installed on the peripheral surface of the handlebar. The shift member is rotatable around the axis of the handlebar. With this device, the thumb of a hand gripping the grip is placed into contact with the peripheral surface of the shift member while rotating the shift member so that a shift cable winding reel takes up the shift cable or returns it so that operating displacement is provided to the derailleur that is connected to the other end of the shift cable.
The grip that is gripped by the palm of the hand and the fingers takes the form of cylindrical member installed concentrically with the handlebar axis, and the cylindrical shift member that is operated by the thumb is also a cylindrical member installed concentrically with the handlebar axis. Thus, the operating displacement of the shift member takes the form of rotational displacement around the axis of the handlebar. However, the sliding motion of the thumb of the hand is a swiveling motion having as its center the joint located at the origin of the thumb, so there is discrepancy between the direction of shift member rotational displacement and the direction of thumb swivel. As a result, it is necessary to shift the hand from the grip in order to rotate the control member by swiveling the thumb, sometimes producing a degree of comfort of operation that is not satisfactory. The discomfort during operation is particularly noticeable when the shift member is rotated to a significant degree in order to produce a large change in shift position.